Opponents of a planned courthouse downgrade have high powered support.

More than 150 people protesting at the site this week were joined by New Zealand First leader Winston Peters. He says "justice is more than a matter of dollars and cents," and that giving National electoral support will only allow the changes.

"Whangarei staff are already under immense pressure and that will only get worse," he says. "The Government will save money but the extra cost will fall on you."

The Ministry of Justice plans to use Dargaville Court for hearings only from early next year. The move is part of a nationwide programme to modernise court services. Graeme Ramsey, head of the steering committee that organised the rally, says he is proud of the Dargaville community.

"For a little town on a Monday morning this was a pretty strong turnout, and it's not people who would normally protest."

Opotiki mayor John Forbes has pledged his support for Kaipara groups uniting to oppose the plan.

In a letter Mr Forbes says he empathises with the groups, having had the same treatment in his own district in recent weeks.

Opotiki District Court was reduced to only six hearing days a month, with the court's paperwork transferred to the Whakatane District Court, meaning counter services were no longer provided from the site.

"There's an argument from the ministers that ‘it's not about cutting services, but about changing the way we access them'.

"It's all good and well to tell someone to go online and fill out a form, but districts like Opotiki and Kaipara face challenges that make this impossible for many of our people," Mr Forbes says.

Northland MP Mike Sabin says the changes are about moving the courts away from a mindset which focuses on the building, and towards a mindset focused on getting court users the services and outcomes they need.

"Hearings in front of a judge will still be held in the Dargaville court," Mr Sabin says.